96 tahoe transmission swap

Ok, so my transmission on the 96 tahoe is shot, it will not shift into 3rd and 4th. I have another 350, with 80k on it, a 4l80e transmission with less than 2k on a rebuild, and the transfer case from a 94 k2500, all still bolted together. In addition to the transmission problem, I now have a head gasket issue, and so I'm thinking of using it all in the tahoe. Doing a little research, I've learned that I will have to re-pin the connector for the pcm, and I'm getting conflicting reports about possibly needing to have the pcm flashed. Should I keep my transfer case, or would it be worth swapping that out? Though it would mean converting from push-button, to manual. And of course modifying my driveshaft. Any thoughts?